Molybdenum metal powders with a defined oxygen content are used for plasma spraying in order to achieve particularly hard spray coatings. Molybdenum wire is preferably employed as the fusible material for flame spraying with an ethine-oxygen mixture. The metal droplets are partly oxidized during flame spraying by this procedure.
See, Gmelin Handbuch der anorganischen Cehmie, Molybdan (Gmelin Handbook of Inorganic Chemistry, Molybdenum), supplement volume part A1, 1977 pages 182 et. seq.
Although processes for the preparation of corresponding oxygen-containing molybdenum metal powder are known, in contrast to flame spraying plasma spraying has still not been able to find acceptance to date for molybdenum for various reasons, since provision of corresponding powders is not guaranteed industrially.
A process for the preparation of oxygen-containing molybdenum powder by an oxidizing plasma treatment is known from U.S. Pat. No. 4,146,388. Three processes for the preparation of oxygen-containing molybdenum spray powder are described in EP-A 233 574. These are treatment of molybdenum metal with dilute hydrogen peroxide solution, thermal treatment of molybdenum metal powder with steam under an inert gas atmosphere and the preparation of agglomerated oxygen-containing molybdenum metal powder using molybdenum oxides. The disadvantage of the molybdenum powders prepared in this way is their imprecisely defined oxygen content. These molybdenum metal powders are moreover often inhomogeneous. Futhermore, these molybdenum metal powders frequently have an MoO.sub.3 content which has an adverse effect on the spraying properties of the powder.